1. Field of the Invention
The present invention relates to a torque measuring device to measure a torque of a rotating body without contact with its rotating portion, and particularly to a torque measuring device, for which an appropriate maintenance work can be timely performed on a light receiving fiber for receiving an optical signal from the rotating body.
2. Description of the Related Art
A torque measuring device for a rotating body is set between a driving shaft powered and a driven shaft loaded and measures a rotating torque without contact with the rotating portion of a rotating body. Such a torque measuring device is disclosed in Japanese Patent Publication No. 2002-22566, which is used, for example, to measure a rotating torque between a measurement roller and a brake system in a chassis dynamo rotated by a wheel of a vehicle.
FIGS. 1A and 1B respectively show a partly cut away and cross-sectioned side view and a partly cut away front view of a conventional torque measuring device for a rotating body.
As shown in FIGS. 1A and 1B, a conventional torque measuring device for a rotating body 50 comprises: a rotary section 51 rotatably disposed between a driving shaft 91 powered and a driven shaft 93 loaded; and a stationary section 55 fixedly disposed so as to surround the rotary section 51. The rotary section 51 integrally comprises: a first flange 52 to be bolted to a driving shaft flange 92 of the driving shaft 91; a second flange 54 to be bolted to a driven shaft flange 94 of the driven shaft 93; and a hollow cylinder 53 having the first and second flanges 52 and 54 formed respectively on both edges thereof. The stationary section 55 comprises: an annulus 56 located so as to surround the second flange 54; and a chassis 57 to which the annulus 56 is fixedly attached via attaching members 58.
A primary coil 82 is provided at the inner circumference of the annulus 56, and a secondary coil 83 is provided at the outer circumference of the second flange 54. The primary and secondary coils 82 and 83 in combination constitute a rotary transformer 81, thereby supplying electric power to the rotary section 51.
Torque detectors 61 as strain gauges are provided at the inner circumference of the cylinder 53, a plurality of light emitting elements 67a to 67n, which are adapted to emit light according to an output from the torque detectors 61 thereby outputting an optical signal, are provided at the outer circumference of the second flange 54 so as to be arrayed along the secondary coil 83, a light receiving fiber 71 for receiving the optical signal from the light emitting elements 67a to 67n is provided along the primary coil 82 on the inner circumference of the annulus 56, and optical-electrical signal converters (not shown) for converting the optical signal into an electrical signal are provided at the ends of the light receiving fiber 71.
In the torque measuring device 50, when the driving shaft 91 rotates, the output from the torque detectors 61 is carried via the light emitting elements 67 and the light receiving fiber 71 to the optical-electrical signal converters (not shown) and is detected thereby, thus measuring a rotary torque.
As described above, the conventional torque measuring device 50 is set between the driving shaft powered and the driven shaft loaded and measures a rotary torque between a rotating body and a load without contact with the rotating shaft or the rotating portion of the rotating body. However, oil mist generation is often involved in the measurement of the torque for a rotating body, and if oil mist adheres to the light receiving fiber 71, it may happen that the measuring accuracy is impaired or even the measurement cannot be performed. Thus, the light receiving fiber 71 is required to be cleaned or replaced as appropriate. It is, however, difficult to determine from the outside the extent of oil mist adhering to the light receiving fiber 71, and in some cases it may happen that a periodical maintenance work does not fulfill its purpose. Specifically, it happens that the measurement cannot be appropriately performed already before a scheduled periodical maintenance work thus indicating “too late”, or that the light receiving fiber 71 is cleaned or replaced when only a small amount of oil mist adheres thereto thus indicating “too early” and therefore resulting in waste of time and labor.